Wireless frequency spectrum is controlled by government bodies. These government bodies allocate the frequency spectrum to particular wireless operators, and place conditions on how the frequency spectrum is used. For example, allocated frequency spectrum is typically required to operate either in a time division duplex (TDD) or frequency division duplex (FDD) mode. In a system that operates using TDD, the uplink and downlink channels share the same frequency band, but are transmitted and received by the base station during mutually exclusive periods of time, as illustrated in FIG. 1. In a system that operates using FDD, the uplink and downlink channels are transmitted simultaneously on different frequency bands, as illustrated in FIG. 2.
In TDD systems additional frequency bands are typically obtained adjacent to existing frequency bands. Accordingly, the TDD channel bandwidth is expanded into the adjacent frequency band. For example, if a TDD system, which operates in a 5 MHz frequency band, obtains an additional 5 MHz frequency band adjacent to the existing frequency band, the frequency bandwidth is expanded to 10 MHz. This expansion is supported in time division code division multiple access (TD-CDMA), which supports a transition from a 5 MHz to 10 MHz frequency band with a chip rate change. Additionally, WiMAX, which supports scalable orthogonal frequency division multiple access (OFDMA), supports frequency bands between 1.25 MHz to 20 MHz through either increasing the tone spacing or the FFT size.
As new frequency spectrum is allocated to wireless network operators, it would be desirable reduce costs associated with adjusting base stations for operation over the newly allocated frequency spectrum.